Description of the Prior Art
Peroxydisulfates have long been known as oxidants for desizing textile goods sized with starch. Austrian Patent No. 281,743 discloses desizing processes which are carried out at a pH of about 10 and use an alkali metal or ammonium peroxydisulfate solution. German Laid-Open Application DOS No. 2,913,177 discloses an oxidative desizing agent consisting of from 10 to 80% by weight of a surfactant and from 20 to 90% by weight of potassium peroxydisulfate. Finally, German Published Application DAS No. 2,814,354 discloses an oxidative desizing process in which peroxydisulfate is used as the desizing agent, together with a water-soluble polymer of acrylic acid.
All these processes have the common feature that the agents must be stored and metered in solid form, since peroxydisulfates lose their activity fairly rapidly in aqueous solution, as a result of decomposition, even if the solution is made weakly alkaline, as would be the case, for example, with the agents disclosed in German Published Application DAS No. 2,814,354.
However, because of the difficult metering technique, solid products, such as peroxydisulfate, or semisolid (pasty) products as disclosed in German Laid-Open Application DOS No. 2,913,177 are not particularly welcomed by the customer.
It is an object of the present invention to convert the peroxydisulfate into a storage-stable, extremely fluid and easily meterable form which, like the solid formulations hitherto proposed, ensures satisfactory or even better oxidative desizing.
We have found that this object is achieved by water-containing suspensions of potassium peroxydisulfate as defined in claims 1 and 2.
We have found, surprisingly, that, in spite of the presence of water, the peroxydisulfate does not decompose in this suspension if the water contains additional potassium ions. These potassium ions evidently have an effect on the solubility product of potassium peroxydisulfate such that the peroxydisulfate becomes virtually insoluble under the conditions of storage in water and is thus in finely disperse form and is not attacked by the water. The peroxydisulfate dissolves, and can become active in the intended sense, only under the desizing conditions, where it is in highly dilute form.
The suspensions according to the invention necessarily contain potassium peroxydisulfate, a polymer or copolymer of acrylic acid and/or maleic acid and the water containing additional potassium ions. The amount of potassium peroxydisulfate in the suspension is preferably from 15 to 40% by weight, in particular from 20 to 30% by weight, based on the suspension.
For the purposes of the invention, polymers or copolymers of acrylic acid or maleic acid are those which are water-soluble, and in particular polyacrylic acid and polymaleic acid themselves, and the copolymers are preferably those which contain, as comonomer units, not more than 50% by weight of monoethylenically unsaturated compounds which can be copolymerized with acrylic acid or maleic anhydride, eg. methacrylic acid and C.sub.1 -C.sub.4 -alkyl acrylates or methacrylates, and copolymers of maleic acid with methyl vinyl ether, vinyl acetate, styrene, acrylic acid or methacrylic acid. Other copolymers are described in the above German Published Application DAS No. 2,814,354, which is hereby incorporated by reference. However, polyacrylic acid and polymaleic acid are of particular industrial interest.
All the polymers should have a Fikentscher K value of from 8 to 30, preferably from 10 to 20, and they are preferably used in amounts of from 2 to 35% by weight, in particular from 9 to 30% by weight.
Preferably, from 5 to 35% by weight of water containing the additional K.sup..sym. ions is required. These ions preferably originate from compounds which supply potassium ions and are capable of assisting in bringing the pH to the required value of not less than 5, ie., in particular, KOH, potassium carbonate or K.sub.2 O. Other compounds, such as K.sub.2 SO.sub.4, potassium phosphate or KCl, may also be used. The aqueous phase contains from 12 to 65% by weight of the potassium compounds, which substantially corresponds to not less than the saturation concentration, ie. the exact percentages depend, within the above limits, on the particular potassium compound used.
This system is a storable liquid suspension which can easily be metered and can successfully be used in desizing liquors.
Suspensions which are still easier to meter, and can even be pumped, are obtained by adding, preferably, not more than 75% by weight, in particular from 25 to 45% by weight, based on the newly formed suspension, of an anionic surfactant conforming to the above definition, in particular a C.sub.8 -C.sub.20 -alkanol half-ester of phosphoric or sulfuric acid, or an oxyethylate thereof containing from 1 to 7 ethylene oxide units. C.sub.10 -C.sub.20 -alkane-sulfonates and alkylbenzenesulfonates and sulfated alkyl-phenolethoxylates are also suitable anionic surfactants. Finally, non-ionic surfactants, in particular C.sub.8 -C.sub.20 -alkanol-oxyethylates containing from 1 to 10 ethylene oxide groups, may also be present, although not exclusively, preferably in an amount of not more than 40% by weight.
The suspensions made up in this manner are very useful as oxidative desizing agents for textile goods sized with starch, and the desizing liquors generally contain from 4 to 20 g/liter, preferably from 6 to 13 g/liter of these suspensions. Depending on the surfactant content of the persulfate suspension, the liquor also contains wetting agents and detergents, but these additional agents may be dispensed with if the surfactant content of the suspension is relatively high.